Described below is a superconducting current-limiter device of the resistive type having at least one bifilar coil winding composed of at least one HTS conductor in the form of a ribbon, with at least one electrically insulating spacer being arranged between adjacent turns of the coil winding, which spacer is transparent for a coolant, at least in subareas. A resistive current-limiter device such as this is disclosed in DE 10 2004 048 646 A1.
Since superconducting metal-oxide compounds have become known, with high critical temperatures Tc of above 77 K, and which are therefore also referred to as high Tc superconductor materials or HTS materials, and which in particular allow liquid-nitrogen (LN2) cooling, attempts have been made to also design superconducting current-limiter devices using corresponding HTS conductors. One such current-limiter device is disclosed in the abovementioned DE-A1 document. This is formed with at least one HTS conductor in the form of a ribbon, which has a metallic, textured support ribbon, in particular a so-called RABiTS ribbon composed of a nickel alloy (cf. “Applied Superconductivity”, Vol. 4, Nos. 10-11, 1996, pages 403 to 427). A layer system composed of oxidic buffer materials, such as CeO2 or Y2O3, and the HTS material, in particular composed of YBa2Cu3Ox (so-called “YBCO”), is deposited on this support ribbon. This structure is also coated with a thin normally conductive covering layer, in order to suppress so-called hotspots (cf. also DE 198 36 860 A1), in which measures are also taken in order to prevent electrical flashovers between the covering layer and the metallic substrate ribbon. A corresponding conductor type is also referred to as a coated conductor. In the case of the known current-limiter device, a spiral bifilar coil winding formed of an HTS ribbon conductor such as this is wound, with good accessibility for the coolant LN2. For this purpose, a spacer in the form of a ribbon and composed of insulating material is also wound in with the HTS ribbon conductor, at the same time ensuring adequate mutual insulation between adjacent coil turns.
WO99/33122 discloses a superconducting current-limiter device of the resistive type which has a superconducting conductor track. The superconducting conductor track is in the form of a bifilar disk winding, with insulating ribbons being located between adjacent ribbon layers of the winding, for electrical insulation. Insulating ribbons such as these may, for example, have a corrugated or ribbed structure.
EP 0 444 792 A2 discloses a superconducting coil of a thin-film superconductor (coated conductor). The thin-film superconductor can be shaped to form a so-called pancake coil. In this case, adjacent turns can be separated from one another by web-like spacing elements which are effectively separated from one another in the extent direction of a support ribbon.
The amount of HTS ribbon conductor material required, and the specific costs, are critical factors for the financial viability of corresponding current-limiter devices. The amount of material is itself governed by the parameters “critical current per width of the (Ic/w)” and the “maximum permissible voltage drop per length of the ribbon (U/L)”. Both parameters should be as high as possible. While the variable Ic/w is governed only by the characteristics and the production method of the superconductor layer, the variable U/L depends on the characteristics of the non-superconducting parts of the layer structure, that is to say in particular on the sub-strate ribbon final temperature of the current-limiter coil winding during a limiting phase (U/L)2 is governed by the product of the sheet resistance and the area-related heat capacity added over all the layers of the conductor structure. For example, for an RABiTS ribbon conductor with a nickel-alloy substrate ribbon, whose thermal mass is formed essentially by the substrate ribbon, the variable U/L is equal to 0.4 V/cm for a switch-off time of 50 ms and a final temperature of 300 K. In another known type of current-limiter device, in which an HTS conductor track is formed on an extended substrate plate composed of sapphire and has a gold covering layer, U/L is in contrast in the range from 9 to 10 V/cm. The reason for this considerably higher value for a “sapphire plate conductor” such as this is that the substrate, which has a high available heat capacity, at the same time produces virtually no Joule heat as an insulator, however.